Method of assembling a mercury button switch



Jan. 18, 1966 w. cooK ETAL 3,229,354

METHOD OF ASSEMBLING A MERCURY BUTTON SWITCH Filed April 24, 1961[aye/Mans: Zea/yard 14/ (00/6, [dward F dad Jam,

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United States Patent Ofifice 3,229,354 Patented Jan. 18, 1966 3,229,354METHOD OF ASSEMBLING A MERCURY BUTTON SWITCH Leonard W. Cook, Varwick,13.1., Edward R. Coutant,

Stratford, Conn, and Arville W. Gilmore, Warwick,

12.1., assignors to General Electric Company, a corporation of New YorkFiled Apr. 24, 1961, Ser. No. 104,939 8 Claims. (Cl. 29155.5)

The present invention relates to a mercury button switch in which theceramic member of the button is bonded to the header, and whicheliminates organic materials from the internal construction.

Cook and Passarelli Patent No. 2,916,589, which is assigned to the sameassignee as the present application, disclosed a mercury button switchin which a cylindrical shell was capped by a retainer ring whichmaintained an axially positioned terminal pin in position by means of anannular glass seal. A ceramic barrier and sealing gasket combined withthe glass seal to insulate the terminal pin from the retaining ring sothat an electrical circuit from the terminal pin had to pass throughmercury positioned in the ceramic barrier to the metal shell. In theconventional mercury button switches manufactured prior to the Cook andPassarelli invention, a pair of symmetrical metal shells were sealedagainst a ceramic barrier by means of a glass seal forming a rim.Because of the differences in coefficients of expansion of the ceramic,metal, and glass, this construction has always offered difiiculties froma manufucturing point of view.

In the switch of the Cook and Passarelli patent, it was necessary thatthe retaining ring he insulatingly sealed from the terminal pin and thiswas accomplished by means of a resilient silicone washer. Not only wasthe silicone material costly, but it introduced a slight quantity oforganic material to the interior of the mercury button. While a siliconecan withstand relatively high temperatures, its presence in an arc pathon the higher cold lamp loads such as a 15-an1pere alternating currentcold lamp load will result in its decomposition. In a mercury buttonthis decomposition can produce end products which are highlydeleterious. Accordingly, one of the objects of the present invention isto produce a mercury button switch which does not contain any organicmaterial in the interior thereof.

Another object of the invention is to produce a mercury button switch inwhich the ceramic barrier of the button is sealed to the header toinsulate the terminals electrically by a bond impervious to liquidmercury and mercury vapor, and mechanically strong enough to withstandnormal handling and thermal shock.

Other objects of the invention will be apparent from the followingspecification and the drawing wherein:

FIG. 1 is a perspective view of a mercury button switch made inaccordance with this invention;

FIG. 2 is a sectional view of the switch illustrated in FIG. 1;

PEG. 3 is an exploded view of the switch illustrated in FIG. 1;

FIG. 4 illustrates in section the apparatus used in direct-bonding theinterior assembly of the mercury button switch illustrated in FIG. 1;and

FIGS. 5, 6, and 7 are broken perspective views of the ceramic barrier ofthe switch illustrated in FIG. 1 showthe present invention is directedto a mercury button vention operates.

Briefly stated, in accordance with one of its aspects, the presentinvention is directed to a mercury button switch comprising a metalshell with a closed terminal end and open end and an axis of rotationthrough the ends. Welded to the shell as a closure assembly tohermetically seal the shell is a retaining ring which is part of theclosure assembly including a central terminal pin sealed in position bymeans of an insulating element such as glass and having a ceramicbarrier directly bonded to this insulating element around their engagingsurfaces. The interior of the button contains a measured quantity ofmercury movable within the ceramic barrier to make and break electricalcontact between the shell and central terminal pin in accordance withthe spatial orientation of the button.

Glass-to-metal bonds and seals are well known and in general areaccomplished either by matching the coeflicients of expansion of themetal and glass or by intentionally mismatching the coefficients as byproviding a metal ring of greater coeflicient of expansion than glasswhich is compressed within the metal ring. Glass-toceramic seals alsorequire a matching of the expansion coefficients and thus the use of asingle glass element as a bond for both a metal and a ceramic becomesdifficult to accomplish. The present production mercury button (see US.Patents 2,101,092; 2,153,000; 2,177,498; and 2,175,306) has agiass-metal-ceramic seal in which the linear coefficients of thermalexpansion are matched while the header of this invention has acompression type seal in the header itself and a matching type for theceramic-to-header bond.

Referring to the drawing, the button switch 10 consists of a cylindricalshell 11 with a closed end 12 and an open end having an outwardlyextending flange 14 with a lip 15. The remaining solid elements of theswitch comprise a terminal metal pin 20 centrally positioned withrespect to a retaining ring 22 by means of a glass seal 21 which ispreferably formed from a preform. Directly bonded to the glass seal 21is a cylindrical ceramic barrier or liner 25 which has an aperturethrough which mercury can flow, as will be explained later. Whendirect-bonded, the pin 20, glass seal 21, retaining ring 22, and barrier25 form an assembly which is sealed, as by welding of the ring 22 to theflange 14, to the shell 11 with the barrier 25 on the interior thereof.

The present invention is directed particularly to the means of bondingand sealing the assembly comprising the terminal pin 20, glass member21, retaining ring 22, and barrier 25 and this invention will bedescribed with reference to this assembly before the remaining elementsof the switch are identified and its operation described.

We have found that if a glass preform is used in making the glass seal21 and the sealing temperature is carefully controlled, not only willthe seal be gas-tight but the bond will be strong enough to withstandrough usage in the field. The preform may be molded into the formillustrated in FIG. 3 to minimize the quantity of glass needed and theglass flow required. In a preferred form it is composed of fine glassparticles mixed with a binder and pressure molded to shape. As shown inFIG. 3, the preform preferably has an annular groove 21a in which anannular protuberance 25a of the barrier 25 seats during the sealingoperation.

The glass preform 21 may be made of relatively soft glass, i.e., glasshaving a relatively low content of silica and magnesia and a relativelyhigh content of sodium oxide and boron oxide. Easily reduced oxides,such as lead oxide, should be omitted from the composition as arcingmight be more deleterious to glass compositions containing such oxides.Glass compositions suitable for making preforms usable in the presentinvention are disclosed in Stanworth Patent No. 2,719,932, which isassigned to the same assignee as the present invention. It isunderstood, however, that glass composition is not particularly criticalin the present invention. The socalled soft glasses melt at a lowertemperature and are therefore easier to work with but glasses havinghigh softening points may also be used. Where the glass preforms used inthis invention are of the powdered type, they are quite porous andtherefore contain quantities of gas. As the preform is heated, thesegases expand and begin to escape. However, when the glass reaches itssoftening point, a glaze is formed and thereafter the gases cannotescape. As a result, the preform expands as the temperature is raisedabove its softening point and this expansion is much greater than wouldbe the case if the gases were not present. Upon expansion, such a glasswill readily bond to an oxidized metal surface or to a ceramic surfacesince the ceramic itself is an oxide even though there is a considerablegap between mating surfaces. On cooling, the glass contracts at adifferential rate down to its softening point as the gases contract butdoes not draw back from an oxide surface which has been wetted by theglass while it was in a molten state. If the initial wetting of thesealing surfaces by the glass was made under compression, the effect ofshrinkage upon cooling is minimized and the mechanical stresses from theshrinking retaining ring 22 aid in developing the ultimate hermetic sealby holding the glass in compression. Thus, we have found that the glasspreform 21 can readily seal and bond the terminal pin 20, retainer ring22, and barrier 25 into an assembly in accordance with the methodoutlined in greater detail hereinafter.

Referring particularly to FIG. 4, in sealing and bonding the pin 20,ring 22, and barrier 25 of this invention by means of the glass preform21, it is desirable that the parts be positioned by means of a carbonblock or fixture 4 and 6. Preferably, the metal ring 22 and terminal pin20 are acid-etched for several minutes (concentrated bydrochloric acidis satisfactory for the metal parts when they are composed ofcold-rolled steel) and carefully rinsed. This etching roughens thesurface of the metal parts to increase the bonding area. The etchedsurface is then oxidized as by heating in air or other oxidizingatmosphere or by contact with an oxidizing agent to promote adherence.The terminal pin 20, glass preform 21, retaining ring 22, and ceramicbarrier 25 are then assembled in the carbon block fixture 4 and 6 asillustrated in FIG. 4. The fixture and parts are then heated, as in anelectric furnace, preferably in a non-oxidizing atmosphere such as thatprovided by dissociated ammonia.

The fixture and parts are preferably first pre-heated for severalminutes at a temperature of about 750 F. The temperature is then raisedto a point 200 F.450 F. above the softening point of the particularglass preform used and maintained at this temperature until the glasspreform has softened and wet the bonding surfaces of the pin 20, ring22, and barrier 25. The conventional soft glass preform temperatureswould normally be 1600 F. to 2000 F. for periods of time ranging from aslow as two minutes to as high as thirty minutes depending on theparticular glass composition used. For a conventional soft glass preforma temperature of 1950 F. for five minutes is suflicient to accomplishthis bonding. During the bonding operation, it is preferable that theparts be maintained in pressure contact with each other. After thebonding is complete, the assembly is cooled slowly to minimize localstresses.

While the single-step bonding and sealing of the parts as describedabove is the preferred form of this invention, it may also be practicedby a two-step process in which the terminal pin 20 and retaining ring 22are first bonded and sealed in accordance with the method describedabove, and the barrier 25 is then bonded and sealed by a reheat step.

Where the glass preform is solid rather than powdered it is preferablethat the preform be subjected to a degree of compression during themolten stage in order to insure intimate contact between the glass andthe metal and ceramic elements. This pressure must be controlled inorder to avoid squeezing the glass through any open spaces.

The principal element of the switch is the ceramic barrier or liner 25which, as best seen in FIG. 2, has a transverse central partition 26which serves to divide the interior of the switch 10 into pools ofmercury 29 and 30. As best shown in FIGS. 5, 6, and 7 the partition 26has a circular opening or port 27 and a reservoir or cavity 28 in oneside thereof. The through opening 27 is designed to permit the mercuryon both sides of the partition to flow together at the center of theopening and complete an electrical circuit between the metal shell 11and the head 23 of the terminal pin 20. It is important that the switchbe capable of operation within a rotational angle of 20 or less.Accordingly, the through opening 27 is located as far as possible fromthe geometric center axis of the metal shell. The reservoir or cavity 28is positioned with its lower edge on a line drawn through the centeraxis of the shell and the center axis of the through opening 27.Referring to FIGS. 6 and 7, as the switch is rotated in acounter-clockwise direction, the through opening 27 will begin to sinkbelow the top level of the mercury pools 29 and 36. This begins toremove the obstruction between the two pools and they enter the throughopening 27 with rounded frontal surfaces 31 and 32, as illustrated inFIG. 6. As these two bodies of liquid mercury come into contact, a highinrush current will immediately vaporize the frontal surfaces of themercury bodies. Final circuit closure might occur only after two or moresuch vaporizations or explosions. The purpose of the reservoir 28 is todump the last traces of mercury into the mercury stream at the opportunemoment when the two pools begin to merge at the center of the throughopening 27. This action increases the kinetic energy of the movingmercury bodies and minimizes the local explosive effects of thecontacting surfaces of mercury. When the switch is turned to opencircuit position, the reservoir 28 again serves to increase the kineticenergy of the moving mercury bodies as they begin to separate. The metalshell 11 has an indexing notch 37 which is utilized for positioning androtating the switch. A complementary notch 38 on the surface of theceramic barrier 25 insures the proper orientation of the barrier 25within the metal shell 11. Prior to the final sealing of the pin 20,ring 22, and barrier 25 assembly and mercury within the shell 11, anon-oxidizing atmosphere is provided within the switch. Preferably thisatmosphere is predominantly argon with hydrogen added for alternatingcurrent operation. For direct current operation, the atmosphere ispreferably predominantly hydrogen and both alternating and directcurrent operation may be at a pressure above atmospheric, e.g., 40pounds per square inch.

In operation, a switch handle (not shown) is seated on the outercylindrical side of the shell 11 in the indexing notch 37 to impartrotary motion within a restricted arc to the mercury button switch.Rotation of the switch produces the opening and closing of the electriccircuit from the terminal pin 20 to the shell 11 by means of the mercurypools 29 and 30, as previously described with reference to FIGS. 5, 6,and 7. While the invention has been described with reference to aparticular embodiment thereof, it is obvious that there may be manyvariations which fall within the true spirit of the invention.Therefore, the invention should be limited in scope only as may benecessitated by the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. The method of making a mercury button switch which comprises: formingpowdered glass containing a binder into a disk with a central aperture;mounting said disk on a metal terminal pin, positioning said pin anddisk in a metal retaining ring horizontally on a support surfaceprovided with a complementary receptacle for the outer extension of saidterminal pin, and positioning a ported ceramic barrier to engage theouter perimeter of said glass disk and the inner perimeter of saidretaining ring and thereby forming a mercury pool; heating the disk,pin, ring, and barrier to a temperature of 200 F. to 500 F. above thesoftening point of the glass disk to direct-bond the parts into anintegral assembly, positioning a quantity of mercury in said pool; andhermetically sealing said assembly in a metal housing by means of saidretaining ring whereby electrical contact between said pin and housingthrough said mercury is controlled by the spatial orientation of saidhousing about its axis horizontally.

2. The method of claim 1 wherein the heating step is carried out in anon-oxidizing atmosphere.

3. The method of claim 2 wherein the atmosphere is dissociated ammonia.

4. The method of claim 1 wherein the glass disk has an annular groovenear the perimeter of the interior side thereof and the ceramic has anannular protuberance which seats in said groove.

5. The method of making a mercury button switch which comprises: formingpowdered glass particles containing a binder into a disk with a centralaperture; mounting said disk on a metal terminal pin and mounting saidpin and disk in a metal retaining ring horizontally on a support surfaceprovided with a complementary receptacle for the outer extension of saidterminal pin; heating said disk, pin, and ring to a temperature abovethe softening point of the glass to expand the gas in said glass to forman intimate bond between said pin and ring and said glass, and coolingsaid pin, ring and glass; positioning a ported ceramic barrier inengagement with the outer perimeter of said glass and the innerperimeter of said ring and thereby forming a mercury pool; heating saidglass, pin, ring, and barrier to a temperature above the softening pointof said glass to direct-bond said glass, pin, ring, and barrier into anassembly and cooling said assembly; positioning a quantity of mercury insaid pool; and hermetically sealing said assembly in a metal housing byattachment of said retaining ring to said housing whereby electricalcontact between said pin and housing through said mercury is controlledby the spatial orientation of said housing about its axis horizontally.

6. The method of claim 5 carried out in an atmosphere of dissociatedammonia.

7. The method of making a mercury button switch which comprises: formingpowdered glass containing a binder into a disk with a central aperture;roughening and lightly oxidizing the surfaces of a metal terminal pinand retaining ring; mounting said glass disk on said pin and positioningsaid pin and disk within said retaining ring horizontally on a supportsurface provided with a complementary receptacle for the outer extensionof said terminal pin; positioning a ported ceramic barrier in engagementwith the abutting surfaces of said disk and ring and thereby forming amercury pool; heating said pin, ring, disk, and barrier above thesoftening point of said disk to enable the gases in said disk to expandthe disk to bond and hermetically seal said pin, disk, ring, and barrierinto an assembly; positioning a quantity of mercury in said pool; andsealing said assembly by means of said retaining ring in a cylindricalmetal shell Whereby electrical contact between said pin and said shellis selectively established through said mercury in accordance with thespatial orientation of said shell about its axis horizontally.

8. The method of claim 7 wherein the atmosphere is dissociated ammonia.

References Cited by the Examiner UNITED STATES PATENTS 1,935,513 11/1933Massey 29--155.55 2,279,168 2/ 1940 Kalischer et al -59 XR 2,458,5521/1949 Blattner 29--155.55 2,504,303 4/ 1950 Clark et al. 6559 2,561,5207/1951 Lemmens et al. 65--59 2,570,095 10/1951 Bucklen et al. 200-1522,597,978 5/1952 Doran 65-59 XR 2,770,923 11/1956 Dalton et a1 65-59 XR2,916,589 12/1959 Cook et al. 200-152 WHITMORE A. WILTZ, PrimaryExaminer.

ROBERT K. SCHAEFER, ARTHUR M. HORTON,

JOHN F. CAMPBELL, Examiners.

1. THE METHOD OF MAKING A MERCURY BUTTOM SWITCH WHICH COMPRISES: FORMINGPOWERED GLASS CONTAINING A BINDER INTO A DISK WITH A CENTRAL APERTURE;MOUNTING SAID DISK ON A METAL TERMINAL PIN, POSITIONING SAID PIN ANDDISK IN A METAL RETAINING RING HORIZONTALLY ON A SUPPORT SURFACEPROVIDED WITH A COMPLEMENTARY RECEPTACLE FOR THE OUTER EXTENSION OF SAIDTERMINAL PIN, AND POSITIONING A PORTED CERAMIC BARRIER TO ENGAGE THEOUTER PERIMETER OF SAID GLASS DISK AND THE INNER PERIMETER OF SAIDRETAINING RING AND THEREBY FORMING A MERCURY POOL; HEATING THE DISK,PIN, RING, AND BARRIER TO A TEMPERATURE OF 200*F. TO 500*F. ABOVE THESOFTENING POINT OF THE GLASS DISK TO DIRECTED-BOND THE PARTS INTO ANINTEGRAL ASSEMBLY, POSITIONING A QUANTITY OF MERCURY IN SAID POOL; ANDHERMETICALLY SEALING SAID ASSEMBLY IN A METAL HOUSING BY MEANS OF SAIDRETAINING RING WHEREBY ELECTRICAL CONTACT BETWEEN SAID PIN AND HOUSINGTHROUGH SAID MERCURY IS CONTROLLED BY THE SPATIAL ORIENTATION OF SAIDHOUSING ABOUT ITS AXIS HORIZONTALLY.